Waste heat is often created as a byproduct of industrial processes where flowing streams of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes utilize heat exchanger devices to capture and recycle waste heat back into the process via other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.
Waste heat can be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic methods are typically steam-based processes that recover and utilize waste heat to generate steam for driving a turbine, turbo, or other expander connected to an electric generator or pump. An organic Rankine cycle utilizes a lower boiling-point working fluid, instead of water, during a traditional Rankine cycle. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbons, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa). More recently, in view of issues such as thermal instability, toxicity, flammability, and production cost of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate non-hydrocarbon working fluids, such as ammonia.
The heat engine systems often utilize a turbopump to circulate the working fluid that captures the waste heat. The turbopump, as well as other rotating equipment used in the systems, typically generates thrust loads that arise from the operating pressures and fluid momentum changes that occur in the system during operation. The turbopump may have operational limitations set or determined by a maximum thrust load that may be applied thereto before the turbopump and/or components thereof become damaged. In high density machinery operating with supercritical fluids, such as supercritical carbon dioxide, the machine power density, pressure rise, and rotating speeds exceed those of standard systems, increasing the likelihood of system damage due to excessive thrust loads and rendering standard thrust bearing design techniques inadequate. Accordingly, in some prior high density machinery, a thrust balance piston technique has been employed. However, such techniques have been found to negatively impact system efficiency.
Therefore, there is a need for systems and methods for balancing the thrust loads present in a heat engine system while overcoming the drawbacks of traditional approaches.